Take-home Exercise 3

To explain factors affecting the resale prices of public housing in Singapore.

1 Objectives

To build hedonic pricing models to explain factors affecting the resale prices of public housing in Singapore. The hedonic price models must be built by using appropriate GWR methods. This study focuses on four-room flat and transaction period from 1st January 2019 to 30th September 2020.

2 Dataset

• data.gov.sg

  • Resale Flat Price
  • Master Plan 2014 Subzone Boundary (Web) in shapefile format (i.e. MP14_SUBZONE_WEB_PL)
  • School Directory and Information

• OneMapAPISG

  • Eldercare
  • Hawker Centres
  • Parks
  • Supermarkets
  • Kindergarten
  • Childcare

• LTA Data Mall

  • Bus Stops
  • MRT Stations

• ValaryLim - Github

  • Shopping Malls

3 Install and Load Packages

packages = c('tidyverse', 'sf', 'spdep', 'tmap', 'ggpubr',
             'corrplot', 'units', 'olsrr', 'plyr',
             'matrixStats', 'GWmodel', 'httr')

for (p in packages){
if(!require(p, character.only = T)){
  install.packages(p)
}
  library(p,character.only = T)
}

Explanation on the uses of each package:

• tidyverse: For data import and tidying. It also consist of several other packages specified below.

  • readr: For importing CSV files
  • dplyr: For data manipulation
  • ggplot2: For plotting graphics

• sf & spdep: For spatial data handling

• tmap: For choropleth mapping

• ggpubr: For arranging tmaps to be side-by-side for easy visualisation

• corrplot: For multivariate data visualisation and analysis

• matrixStats & units: For matrix manipulation

• olsrr: For building OLS and performing diagnostics tests

• plyr: For easy data manipulation

• GWmodel: For calibrating geographical weighted family of models

• httr: For API calls

4 Data Import and Preparation for Geospatial Dataset

In this section, we have to import and ensure that the geospatial data is in a format that we can use to perform analysis. We have to check if it is being assigned the right CRS and code. Also, since we are working in the boundary of Singapore, we have to ensure that it is in SVY21 with the EPSG code of 3414 being assigned as well.

The datasets that we will prepare in this section are:

• Singapore’s boundary: MP14_SUBZONE_WEB_PL
• MRT: MRTLRTStnPtt
• Bus stops: BusStop

4.1 Import geospatial data set

• All of the datasets are currently in ESRI shapefile format
• st_read() of sf package to import the geospatial data set.
• The imported shapefile will be a simple feature object of sf.

mpsz_sf <- st_read(dsn = "data/geospatial", layer = "MP14_SUBZONE_WEB_PL")

Reading layer `MP14_SUBZONE_WEB_PL' from data source 
  `C:\wlwong2018\IS415 Blog\_posts\2021-11-06-take-home-exercise-3\data\geospatial' 
  using driver `ESRI Shapefile'
Simple feature collection with 323 features and 15 fields
Geometry type: MULTIPOLYGON
Dimension:     XY
Bounding box:  xmin: 2667.538 ymin: 15748.72 xmax: 56396.44 ymax: 50256.33
Projected CRS: SVY21

mrt_sf <- st_read(dsn = "data/geospatial", layer = "MRTLRTStnPtt")

Reading layer `MRTLRTStnPtt' from data source 
  `C:\wlwong2018\IS415 Blog\_posts\2021-11-06-take-home-exercise-3\data\geospatial' 
  using driver `ESRI Shapefile'
Simple feature collection with 185 features and 3 fields
Geometry type: POINT
Dimension:     XY
Bounding box:  xmin: 6138.311 ymin: 27555.06 xmax: 45254.86 ymax: 47854.2
Projected CRS: SVY21

bus_sf <- st_read(dsn = "data/geospatial", layer = "BusStop")

Reading layer `BusStop' from data source 
  `C:\wlwong2018\IS415 Blog\_posts\2021-11-06-take-home-exercise-3\data\geospatial' 
  using driver `ESRI Shapefile'
Simple feature collection with 5156 features and 3 fields
Geometry type: POINT
Dimension:     XY
Bounding box:  xmin: 4427.938 ymin: 26482.1 xmax: 48282.5 ymax: 52983.82
Projected CRS: SVY21

4.2 Look into datasets

• glimpse() of dplyr package to take a look at our datasets

glimpse(mpsz_sf)

Rows: 323
Columns: 16
$ OBJECTID   <int> 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15~
$ SUBZONE_NO <int> 1, 1, 3, 8, 3, 7, 9, 2, 13, 7, 12, 6, 1, 5, 1, 1,~
$ SUBZONE_N  <chr> "MARINA SOUTH", "PEARL'S HILL", "BOAT QUAY", "HEN~
$ SUBZONE_C  <chr> "MSSZ01", "OTSZ01", "SRSZ03", "BMSZ08", "BMSZ03",~
$ CA_IND     <chr> "Y", "Y", "Y", "N", "N", "N", "N", "Y", "N", "N",~
$ PLN_AREA_N <chr> "MARINA SOUTH", "OUTRAM", "SINGAPORE RIVER", "BUK~
$ PLN_AREA_C <chr> "MS", "OT", "SR", "BM", "BM", "BM", "BM", "SR", "~
$ REGION_N   <chr> "CENTRAL REGION", "CENTRAL REGION", "CENTRAL REGI~
$ REGION_C   <chr> "CR", "CR", "CR", "CR", "CR", "CR", "CR", "CR", "~
$ INC_CRC    <chr> "5ED7EB253F99252E", "8C7149B9EB32EEFC", "C35FEFF0~
$ FMEL_UPD_D <date> 2014-12-05, 2014-12-05, 2014-12-05, 2014-12-05, ~
$ X_ADDR     <dbl> 31595.84, 28679.06, 29654.96, 26782.83, 26201.96,~
$ Y_ADDR     <dbl> 29220.19, 29782.05, 29974.66, 29933.77, 30005.70,~
$ SHAPE_Leng <dbl> 5267.381, 3506.107, 1740.926, 3313.625, 2825.594,~
$ SHAPE_Area <dbl> 1630379.3, 559816.2, 160807.5, 595428.9, 387429.4~
$ geometry   <MULTIPOLYGON [m]> MULTIPOLYGON (((31495.56 30..., MULT~

glimpse(mrt_sf)

Rows: 185
Columns: 4
$ OBJECTID <dbl> 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, ~
$ STN_NAME <chr> "EUNOS MRT STATION", "CHINESE GARDEN MRT STATION", ~
$ STN_NO   <chr> "EW7", "EW25", "NS14", "NS7", "EW18", "NS5", "EW28"~
$ geometry <POINT [m]> POINT (35782.96 33560.08), POINT (16790.75 36~

glimpse(bus_sf)

Rows: 5,156
Columns: 4
$ BUS_STOP_N <chr> "78221", "63359", "64141", "83139", "55231", "553~
$ BUS_ROOF_N <chr> "B06", "B01", "B13", "B07", "B02", "B03", "B10", ~
$ LOC_DESC   <chr> "BLK 231A CP", "HOUGANG SWIM CPLX", "AFT JLN TELA~
$ geometry   <POINT [m]> POINT (42227.96 39563.16), POINT (34065.75 ~

Results above show that:

• There are 323 multi-polygon features and 16 fields in the mpsz_sf sf data frame.
• There are 185 point features and 4 fields in the mrt_sf sf data frame.
• There are 5,156 point features and 4 fields in the bus_sf sf data frame.
• SVY21 is the Projected Coordinates Reference System for all data sets.

4.3 Check for NA values

• rowSums() and is.na() of Base R to check for NA values

mpsz_sf[rowSums(is.na(mpsz_sf))!=0,]

Simple feature collection with 0 features and 15 fields
Bounding box:  xmin: NA ymin: NA xmax: NA ymax: NA
Projected CRS: SVY21
 [1] OBJECTID   SUBZONE_NO SUBZONE_N  SUBZONE_C  CA_IND     PLN_AREA_N
 [7] PLN_AREA_C REGION_N   REGION_C   INC_CRC    FMEL_UPD_D X_ADDR    
[13] Y_ADDR     SHAPE_Leng SHAPE_Area geometry  
<0 rows> (or 0-length row.names)

mrt_sf[rowSums(is.na(mrt_sf))!=0,]

Simple feature collection with 0 features and 3 fields
Bounding box:  xmin: NA ymin: NA xmax: NA ymax: NA
Projected CRS: SVY21
[1] OBJECTID STN_NAME STN_NO   geometry
<0 rows> (or 0-length row.names)

bus_sf[rowSums(is.na(bus_sf))!=0,]

Simple feature collection with 1 feature and 3 fields
Geometry type: POINT
Dimension:     XY
Bounding box:  xmin: 22616.75 ymin: 47793.68 xmax: 22616.75 ymax: 47793.68
Projected CRS: SVY21
    BUS_STOP_N BUS_ROOF_N LOC_DESC                  geometry
264      47201        UNK     <NA> POINT (22616.75 47793.68)

Results above show that:

• mpsz_sf and mrt_sf has no NA values
• bus_sf has 1 NA value

4.4 Remove NA values

• rowSums() and is.na() of Base R to remove NA values

bus_sf <- bus_sf[!rowSums(is.na(bus_sf))!=0,]

4.5 Check for NA values

• rowSums() and is.na() of Base R to check for NA values

mpsz_sf[rowSums(is.na(mpsz_sf))!=0,]

Simple feature collection with 0 features and 15 fields
Bounding box:  xmin: NA ymin: NA xmax: NA ymax: NA
Projected CRS: SVY21
 [1] OBJECTID   SUBZONE_NO SUBZONE_N  SUBZONE_C  CA_IND     PLN_AREA_N
 [7] PLN_AREA_C REGION_N   REGION_C   INC_CRC    FMEL_UPD_D X_ADDR    
[13] Y_ADDR     SHAPE_Leng SHAPE_Area geometry  
<0 rows> (or 0-length row.names)

mrt_sf[rowSums(is.na(mrt_sf))!=0,]

Simple feature collection with 0 features and 3 fields
Bounding box:  xmin: NA ymin: NA xmax: NA ymax: NA
Projected CRS: SVY21
[1] OBJECTID STN_NAME STN_NO   geometry
<0 rows> (or 0-length row.names)

bus_sf[rowSums(is.na(bus_sf))!=0,]

Simple feature collection with 0 features and 3 fields
Bounding box:  xmin: NA ymin: NA xmax: NA ymax: NA
Projected CRS: SVY21
[1] BUS_STOP_N BUS_ROOF_N LOC_DESC   geometry  
<0 rows> (or 0-length row.names)

Results above show that:

• There are no longer any NA values

4.6 Check for duplicate values

• duplicated() of Base R to check for duplicated values

mrt_sf[duplicated(mrt_sf$STN_NAME),]

Simple feature collection with 19 features and 3 fields
Geometry type: POINT
Dimension:     XY
Bounding box:  xmin: 22949.03 ymin: 28735.78 xmax: 42362.71 ymax: 46418.56
Projected CRS: SVY21
First 10 features:
    OBJECTID                STN_NAME STN_NO                  geometry
33        33  ANG MO KIO MRT STATION   NS16 POINT (29807.27 39105.77)
97       105  MACPHERSON MRT STATION   DT26  POINT (34235.8 34256.43)
103      111       BUGIS MRT STATION   EW12 POINT (30491.56 31424.35)
114      122        EXPO MRT STATION   DT35 POINT (42362.71 35285.67)
116      124 BUONA VISTA MRT STATION   CC22 POINT (23251.76 32090.77)
121      129  MARINA BAY MRT STATION    CE2 POINT (30423.43 28735.78)
124      132   CHINATOWN MRT STATION   DT19 POINT (29238.97 29686.54)
134      142    TAMPINES MRT STATION   DT32 POINT (40213.03 37463.37)
140      148   SERANGOON MRT STATION   NE12 POINT (32480.07 36869.39)
144      152  PAYA LEBAR MRT STATION    CC9 POINT (34550.58 33300.34)

bus_sf[duplicated(bus_sf$BUS_STOP_N),]

Simple feature collection with 13 features and 3 fields
Geometry type: POINT
Dimension:     XY
Bounding box:  xmin: 13488.02 ymin: 29969.22 xmax: 44144.57 ymax: 47806.75
Projected CRS: SVY21
First 10 features:
     BUS_STOP_N BUS_ROOF_N             LOC_DESC
350       58031        UNK      OPP CANBERRA DR
1569      51071        B21 MACRITCHIE RESERVOIR
2208      82221        B01               Blk 3A
2215      97079        B14  OPP ST. JOHN'S CRES
2392      62251        B03         BEF BLK 471B
2462      22501        B02             BLK 662A
2736      16119        NIL        TELETECH PARK
2976      58229       B01A          BLK 358A CP
3442      67421        NIL CHENG LIM STN EXIT B
3521      68091        B08         AFT BAKER ST
                      geometry
350   POINT (27089.69 47570.9)
1569 POINT (28305.37 36036.67)
2208 POINT (35308.74 33335.17)
2215 POINT (44144.57 38980.25)
2392 POINT (35500.36 39943.34)
2462 POINT (13488.02 35537.88)
2736 POINT (22318.89 29969.22)
2976 POINT (26094.86 47806.75)
3442 POINT (34741.77 42004.21)
3521 POINT (32038.84 43298.68)

Results above show that:

• There are 19 duplicated values in mrt_sf
• There are 16 duplicated values in bus_sf

4.7 Remove duplicated values

• duplicated() of Base R to remove duplicated values

mrt_sf <- mrt_sf[!duplicated(mrt_sf$STN_NAME),]
bus_sf <- bus_sf[!duplicated(bus_sf$BUS_STOP_N),]

4.8 Check for duplicated values

• duplicated() of Base R to check for duplicated values

mrt_sf[duplicated(mrt_sf$STN_NAME),]

Simple feature collection with 0 features and 3 fields
Bounding box:  xmin: NA ymin: NA xmax: NA ymax: NA
Projected CRS: SVY21
[1] OBJECTID STN_NAME STN_NO   geometry
<0 rows> (or 0-length row.names)

bus_sf[duplicated(bus_sf$BUS_STOP_N),]

Simple feature collection with 0 features and 3 fields
Bounding box:  xmin: NA ymin: NA xmax: NA ymax: NA
Projected CRS: SVY21
[1] BUS_STOP_N BUS_ROOF_N LOC_DESC   geometry  
<0 rows> (or 0-length row.names)

Results above show that:

• There are no longer any duplicated values in both datasets.

4.9 Check CRS

• Check CRS using st_crs() of sf package.
• Singapore is using SVY21.

st_crs(mpsz_sf)

Coordinate Reference System:
  User input: SVY21 
  wkt:
PROJCRS["SVY21",
    BASEGEOGCRS["SVY21[WGS84]",
        DATUM["World Geodetic System 1984",
            ELLIPSOID["WGS 84",6378137,298.257223563,
                LENGTHUNIT["metre",1]],
            ID["EPSG",6326]],
        PRIMEM["Greenwich",0,
            ANGLEUNIT["Degree",0.0174532925199433]]],
    CONVERSION["unnamed",
        METHOD["Transverse Mercator",
            ID["EPSG",9807]],
        PARAMETER["Latitude of natural origin",1.36666666666667,
            ANGLEUNIT["Degree",0.0174532925199433],
            ID["EPSG",8801]],
        PARAMETER["Longitude of natural origin",103.833333333333,
            ANGLEUNIT["Degree",0.0174532925199433],
            ID["EPSG",8802]],
        PARAMETER["Scale factor at natural origin",1,
            SCALEUNIT["unity",1],
            ID["EPSG",8805]],
        PARAMETER["False easting",28001.642,
            LENGTHUNIT["metre",1],
            ID["EPSG",8806]],
        PARAMETER["False northing",38744.572,
            LENGTHUNIT["metre",1],
            ID["EPSG",8807]]],
    CS[Cartesian,2],
        AXIS["(E)",east,
            ORDER[1],
            LENGTHUNIT["metre",1,
                ID["EPSG",9001]]],
        AXIS["(N)",north,
            ORDER[2],
            LENGTHUNIT["metre",1,
                ID["EPSG",9001]]]]

st_crs(mrt_sf)

Coordinate Reference System:
  User input: SVY21 
  wkt:
PROJCRS["SVY21",
    BASEGEOGCRS["SVY21[WGS84]",
        DATUM["World Geodetic System 1984",
            ELLIPSOID["WGS 84",6378137,298.257223563,
                LENGTHUNIT["metre",1]],
            ID["EPSG",6326]],
        PRIMEM["Greenwich",0,
            ANGLEUNIT["Degree",0.0174532925199433]]],
    CONVERSION["unnamed",
        METHOD["Transverse Mercator",
            ID["EPSG",9807]],
        PARAMETER["Latitude of natural origin",1.36666666666667,
            ANGLEUNIT["Degree",0.0174532925199433],
            ID["EPSG",8801]],
        PARAMETER["Longitude of natural origin",103.833333333333,
            ANGLEUNIT["Degree",0.0174532925199433],
            ID["EPSG",8802]],
        PARAMETER["Scale factor at natural origin",1,
            SCALEUNIT["unity",1],
            ID["EPSG",8805]],
        PARAMETER["False easting",28001.642,
            LENGTHUNIT["metre",1],
            ID["EPSG",8806]],
        PARAMETER["False northing",38744.572,
            LENGTHUNIT["metre",1],
            ID["EPSG",8807]]],
    CS[Cartesian,2],
        AXIS["(E)",east,
            ORDER[1],
            LENGTHUNIT["metre",1,
                ID["EPSG",9001]]],
        AXIS["(N)",north,
            ORDER[2],
            LENGTHUNIT["metre",1,
                ID["EPSG",9001]]]]

st_crs(bus_sf)

Coordinate Reference System:
  User input: SVY21 
  wkt:
PROJCRS["SVY21",
    BASEGEOGCRS["WGS 84",
        DATUM["World Geodetic System 1984",
            ELLIPSOID["WGS 84",6378137,298.257223563,
                LENGTHUNIT["metre",1]],
            ID["EPSG",6326]],
        PRIMEM["Greenwich",0,
            ANGLEUNIT["Degree",0.0174532925199433]]],
    CONVERSION["unnamed",
        METHOD["Transverse Mercator",
            ID["EPSG",9807]],
        PARAMETER["Latitude of natural origin",1.36666666666667,
            ANGLEUNIT["Degree",0.0174532925199433],
            ID["EPSG",8801]],
        PARAMETER["Longitude of natural origin",103.833333333333,
            ANGLEUNIT["Degree",0.0174532925199433],
            ID["EPSG",8802]],
        PARAMETER["Scale factor at natural origin",1,
            SCALEUNIT["unity",1],
            ID["EPSG",8805]],
        PARAMETER["False easting",28001.642,
            LENGTHUNIT["metre",1],
            ID["EPSG",8806]],
        PARAMETER["False northing",38744.572,
            LENGTHUNIT["metre",1],
            ID["EPSG",8807]]],
    CS[Cartesian,2],
        AXIS["(E)",east,
            ORDER[1],
            LENGTHUNIT["metre",1,
                ID["EPSG",9001]]],
        AXIS["(N)",north,
            ORDER[2],
            LENGTHUNIT["metre",1,
                ID["EPSG",9001]]]]

From the results above:

• Referencing from epsg.io, the EPSG code of SVY21 is supposed to be 3414.
• The EPSG code shown is 9001 which is incorrect.

4.10 Assign CRS and check again

• st_set_crs() of sf package to assign correct EPSG code to SpatialPointsDataFrame.
• Do not have to use st_transform() since it is already in SVY21.
• st_crs() of sf package to verify the CRS again.

mpsz_sf <- st_set_crs(mpsz_sf, 3414)
mrt_sf <- st_set_crs(mrt_sf, 3414)
bus_sf <- st_set_crs(bus_sf, 3414)

st_crs(mpsz_sf)

Coordinate Reference System:
  User input: EPSG:3414 
  wkt:
PROJCRS["SVY21 / Singapore TM",
    BASEGEOGCRS["SVY21",
        DATUM["SVY21",
            ELLIPSOID["WGS 84",6378137,298.257223563,
                LENGTHUNIT["metre",1]]],
        PRIMEM["Greenwich",0,
            ANGLEUNIT["degree",0.0174532925199433]],
        ID["EPSG",4757]],
    CONVERSION["Singapore Transverse Mercator",
        METHOD["Transverse Mercator",
            ID["EPSG",9807]],
        PARAMETER["Latitude of natural origin",1.36666666666667,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8801]],
        PARAMETER["Longitude of natural origin",103.833333333333,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8802]],
        PARAMETER["Scale factor at natural origin",1,
            SCALEUNIT["unity",1],
            ID["EPSG",8805]],
        PARAMETER["False easting",28001.642,
            LENGTHUNIT["metre",1],
            ID["EPSG",8806]],
        PARAMETER["False northing",38744.572,
            LENGTHUNIT["metre",1],
            ID["EPSG",8807]]],
    CS[Cartesian,2],
        AXIS["northing (N)",north,
            ORDER[1],
            LENGTHUNIT["metre",1]],
        AXIS["easting (E)",east,
            ORDER[2],
            LENGTHUNIT["metre",1]],
    USAGE[
        SCOPE["Cadastre, engineering survey, topographic mapping."],
        AREA["Singapore - onshore and offshore."],
        BBOX[1.13,103.59,1.47,104.07]],
    ID["EPSG",3414]]

st_crs(mrt_sf)

Coordinate Reference System:
  User input: EPSG:3414 
  wkt:
PROJCRS["SVY21 / Singapore TM",
    BASEGEOGCRS["SVY21",
        DATUM["SVY21",
            ELLIPSOID["WGS 84",6378137,298.257223563,
                LENGTHUNIT["metre",1]]],
        PRIMEM["Greenwich",0,
            ANGLEUNIT["degree",0.0174532925199433]],
        ID["EPSG",4757]],
    CONVERSION["Singapore Transverse Mercator",
        METHOD["Transverse Mercator",
            ID["EPSG",9807]],
        PARAMETER["Latitude of natural origin",1.36666666666667,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8801]],
        PARAMETER["Longitude of natural origin",103.833333333333,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8802]],
        PARAMETER["Scale factor at natural origin",1,
            SCALEUNIT["unity",1],
            ID["EPSG",8805]],
        PARAMETER["False easting",28001.642,
            LENGTHUNIT["metre",1],
            ID["EPSG",8806]],
        PARAMETER["False northing",38744.572,
            LENGTHUNIT["metre",1],
            ID["EPSG",8807]]],
    CS[Cartesian,2],
        AXIS["northing (N)",north,
            ORDER[1],
            LENGTHUNIT["metre",1]],
        AXIS["easting (E)",east,
            ORDER[2],
            LENGTHUNIT["metre",1]],
    USAGE[
        SCOPE["Cadastre, engineering survey, topographic mapping."],
        AREA["Singapore - onshore and offshore."],
        BBOX[1.13,103.59,1.47,104.07]],
    ID["EPSG",3414]]

st_crs(bus_sf)

Coordinate Reference System:
  User input: EPSG:3414 
  wkt:
PROJCRS["SVY21 / Singapore TM",
    BASEGEOGCRS["SVY21",
        DATUM["SVY21",
            ELLIPSOID["WGS 84",6378137,298.257223563,
                LENGTHUNIT["metre",1]]],
        PRIMEM["Greenwich",0,
            ANGLEUNIT["degree",0.0174532925199433]],
        ID["EPSG",4757]],
    CONVERSION["Singapore Transverse Mercator",
        METHOD["Transverse Mercator",
            ID["EPSG",9807]],
        PARAMETER["Latitude of natural origin",1.36666666666667,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8801]],
        PARAMETER["Longitude of natural origin",103.833333333333,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8802]],
        PARAMETER["Scale factor at natural origin",1,
            SCALEUNIT["unity",1],
            ID["EPSG",8805]],
        PARAMETER["False easting",28001.642,
            LENGTHUNIT["metre",1],
            ID["EPSG",8806]],
        PARAMETER["False northing",38744.572,
            LENGTHUNIT["metre",1],
            ID["EPSG",8807]]],
    CS[Cartesian,2],
        AXIS["northing (N)",north,
            ORDER[1],
            LENGTHUNIT["metre",1]],
        AXIS["easting (E)",east,
            ORDER[2],
            LENGTHUNIT["metre",1]],
    USAGE[
        SCOPE["Cadastre, engineering survey, topographic mapping."],
        AREA["Singapore - onshore and offshore."],
        BBOX[1.13,103.59,1.47,104.07]],
    ID["EPSG",3414]]

Results above show that:

• The correct EPSG code of 3414 is being assigned

4.11 Check for invalid geometries

• st_is_valid() of sf package is used to check for any invalid geometries.
• length() of Base R to count the number of invalid geometries.

length(which(st_is_valid(mpsz_sf) == FALSE))

[1] 9

length(which(st_is_valid(mrt_sf) == FALSE))

[1] 0

length(which(st_is_valid(bus_sf) == FALSE))

[1] 0

Results above show that:

• mpsz_sf has 9 invalid geometries
• mrt_sf and bus_sf has 0 invalid geometries
• Hence, we have to handle these invalid geometries

4.12 Handle the invalid geometries and check again

• st_make_valid() of sf package to handle the invalid geometries in mpsz_sf.
• st_is_valid() of sf package is used to verify that there are no longer any invalid geometries.

mpsz_sf <- st_make_valid(mpsz_sf)

length(which(st_is_valid(mpsz_sf) == FALSE))

[1] 0

length(which(st_is_valid(mrt_sf) == FALSE))

[1] 0

length(which(st_is_valid(bus_sf) == FALSE))

[1] 0

Results above show that:

• There are no longer any invalid geometries.

4.13 Plot geospatial data

• Reveal the distribution of HDB resale units prices in Singapore

• Create an interactive point symbol map using tmap_mode(“view”)

• tm_dots():

  • Set alpha value to 0.4,
  • colour to blue
  • size of dots to 0.03

• Lastly, tmap_mode(“plot”) to display plot mode

tmap_mode('view')
tm_shape(mpsz_sf) +
  tm_polygons() +
tm_shape(bus_sf) +
  tm_dots(alpha = 0.4,
          col = "blue",
          size = 0.03)

tmap_mode('plot')

Results above show that:

• There are about bus stops that are outside of Singapore’s boundary, namely, 46239, 46609, 47701, 46211, 46219
  
• There are designated bus stops located at Johor Bahru as we are able to travel to and fro Johor Bahru with specific buses.
• Hence, we should remove these bus stops before moving on with our analysis since they are not within Singapore boundary.

4.14 Remove bus stops outside of Singapore boundary

4.14.1 Inspect names of bus stop

• Save the bus stops identified in Section 4.13 in a list
• Inspect names of bus stop

remove_busstop <- list(46211, 46219, 46239, 46609, 47701)
bus_sf[bus_sf$BUS_STOP_N %in% remove_busstop, ]

Simple feature collection with 5 features and 3 fields
Geometry type: POINT
Dimension:     XY
Bounding box:  xmin: 17969.14 ymin: 49173.42 xmax: 20723.24 ymax: 52983.82
Projected CRS: SVY21 / Singapore TM
     BUS_STOP_N BUS_ROOF_N            LOC_DESC
765       47701        NIL          JB SENTRAL
1532      46239         NA          LARKIN TER
2257      46609         NA     KOTARAYA II TER
2269      46211        NIL JOHOR BAHRU CHECKPT
4346      46219        NIL JOHOR BAHRU CHECKPT
                      geometry
765  POINT (20370.54 49173.42)
1532 POINT (17969.14 52983.82)
2257  POINT (20025.46 49261.6)
2269 POINT (20623.18 49199.99)
4346 POINT (20723.24 49200.05)

Results above show that:

• The names of these bus stops shows that the bus stops locations indeed are in Johor Bahru.

4.14.2 Remove bus stops from bus stop data

• Remove bus stops as long as they are in remove_busstop, identified in Section 4.14.1

bus_sf <- bus_sf[!bus_sf$BUS_STOP_N %in% remove_busstop, ]

4.14.3 Check if bus stops are removed

bus_sf[bus_sf$BUS_STOP_N %in% remove_busstop, ]

Simple feature collection with 0 features and 3 fields
Bounding box:  xmin: NA ymin: NA xmax: NA ymax: NA
Projected CRS: SVY21 / Singapore TM
[1] BUS_STOP_N BUS_ROOF_N LOC_DESC   geometry  
<0 rows> (or 0-length row.names)

Results above show that:

• The identified bus stops have been removed.

5 Data Import and Preparation of Aspatial Dataset

In this section, we will prepare the aspatial data sets which will be our independent variables for calibrating the hedonic pricing models in the later section.

Note: This section will not be ran to save computational time. Documentation on the *results are still written even though the output is not shown.

The datasets that we will prepare in this section are:

• Resale that consists of preparing floor level and remaining lease.
• Eldercare
• Hawker centres
• Park
• Primary school
• Shopping mall
• Supermarket
• Kindergartens
• Childcare centres

5.1 Import aspatial data sets

• read_csv() of readr package to import the aspatial data sets.

resale <- read_csv("data/aspatial/resale-flat-prices-based-on-registration-date-from-jan-2017-onwards.csv")
eldercare <- read_csv("data/aspatial/eldercare.csv")
hawker <- read_csv("data/aspatial/hawkercentre.csv")
park <- read_csv("data/aspatial/park.csv")
prisch <- read_csv("data/aspatial/general-information-of-schools.csv")
mall <- read_csv("data/aspatial/mall.csv")
supermarket <- read_csv("data/aspatial/supermarkets.csv")
kindergarten <- read_csv("data/aspatial/kindergarten.csv")
childcare <- read_csv("data/aspatial/childcare.csv")

5.2 Look into datasets

• glimpse() of dplyr package to take a look at our datasets

glimpse(resale)
glimpse(eldercare)
glimpse(hawker)
glimpse(park)
glimpse(prisch)
glimpse(mall)
glimpse(supermarket)
glimpse(kindergarten)
glimpse(childcare)

Results above show that:

• There are 110,893 rows and 11 columns in resale data set.
• There are 133 rows and 6 columns in eldercare data set.
• There are 125 rows and 24 columns in hawker data set.
• There are 352 rows and 8 columns in park data set.
• There are 346 rows and 31 columns in prisch data set.
• There are 184 rows and 3 columns in mall data set.
• There are 526 rows and 9 columns in supermarket data set.
• There are 448 rows and 7 columns in kindergarten data set.
• There are 1545 rows and 7 columns in childcare data set.

5.3 Extract and filter necessary columns and data

• filter() of dplyr package to filter relevant data from resale since this study only focuses on four-room flat and transaction period from 1st January 2019 to 30th September 2020.
• filter() is used again to filter prisch since we are only interested in primary schools.
• select() of dplyr package to extract the necessary columns

resale <- resale %>%
  filter(flat_type == "4 ROOM",
         month >= "2019-01" & month <= "2020-09")

eldercare <- eldercare %>%
  select(NAME, Lng, Lat)

hawker <- hawker %>%
  select(NAME, Lng, Lat)

park <- park %>%
  select(NAME, Lng, Lat)

prisch <- prisch %>%
  filter(mainlevel_code == "PRIMARY") %>%
  select(school_name, address, gifted_ind)
  
supermarket <- supermarket %>%
  select(NAME, Lng, Lat)

kindergarten <- kindergarten %>%
  select(NAME, Lng, Lat)

childcare <- childcare %>%
  select(NAME, Lng, Lat)

5.4 Look into datasets again

• glimpse() of dplyr package to take a look at our datasets

glimpse(resale)
glimpse(eldercare)
glimpse(hawker)
glimpse(park)
glimpse(prisch)
glimpse(mall)
glimpse(supermarket)
glimpse(kindergarten)
glimpse(childcare)
# glimpse(bus)

Results above show that:

• Notice that the number of rows and columns have changed after filtering and selecting
• There are 15901 rows and 11 columns in resale data set.
• There are 133 rows and 3 columns in eldercare data set.
• There are 125 rows and 3 columns in hawker data set.
• There are 352 rows and 3 columns in park data set.
• There are 182 rows and 3 columns in prisch data set.
• There are 184 rows and 3 columns in mall data set.
• There are 526 rows and 3 columns in supermarket data set.
• There are 448 rows and 3 columns in kindergarten data set.
• There are 1545 rows and 3 columns in childcare data set.

5.5 Check for NA values

• is.na() of Base R to check for NA values.
• rowSums() of Base R to sum the number of NA values.

resale[rowSums(is.na(resale))!=0,]
eldercare[rowSums(is.na(eldercare))!=0,]
hawker[rowSums(is.na(hawker))!=0,]
park[rowSums(is.na(park))!=0,]
prisch[rowSums(is.na(prisch))!=0,]
mall[rowSums(is.na(mall))!=0,]
supermarket[rowSums(is.na(supermarket))!=0,]
kindergarten[rowSums(is.na(kindergarten))!=0,]
childcare[rowSums(is.na(childcare))!=0,]

Results above show that:

• All data sets do not contain any NA values

5.6 Prepare resale Dataset

resale dataset has a section on its own as there are different preparation steps to be done:

• Geo-code to extract its latitude and longitude
• Prepare storey_range and remaining_lease columns

5.6.1 Rename value in column

• OneMapApi can only geo code if value is replaced to SAINT
• gsub() of Base R to replace value in column, street_name

resale$street_name <- gsub("ST\\.", "SAINT", resale$street_name)

5.6.2 Combine columns for geo-coding

• mutate() of dplyr package to create a new column namely address, containing block and street_name columns with a space as a separator.

resale <- resale %>%
  mutate(`address` = paste(`block`, `street_name`, sep=' '))

5.6.3 Onemap API for geo-coding

5.6.3.1 Function to geo code

This function does the following:

• Specifies the URL for the API
• Defines search query
• GET() of httr package to extract the request output
• content() of httr package to extract content from the request output
• as.data.frame() of Base R to convert the request to a dataframe
• select() of dplyr package to select the columns: X, Y coordinates, Longitude and Latitude
• Returns the above as a datafame in the output variable

library(httr)

geo_code <- function(address) {
  url <- "https://developers.onemap.sg/commonapi/search"
  query <- list("searchVal" = address, "returnGeom" = "Y", "getAddrDetails" = "N") #, "pageNum" = "1"
  res <- GET(url, query = query, verbose())

  output <- content(res) %>%
    as.data.frame() %>%
    select(results.X, results.Y, results.LONGITUDE, results.LATITUDE)

  return(output)
}

5.6.3.2 For loop to apply function (row 1 to 1000)

This code chunk:

• Assigns 0 to the X, Y coordinates, Longitude and Latitude column in resale
• For loop to apply geo_code function defined in Section 5.6.3.1 on the resale dataset, from row 1 to 1000
• Assigns the extracted X, Y coordinates, Longitude and Latitude into the respective columns.

resale$X <- 0
resale$Y <- 0
resale$LONGITUDE <- 0 
resale$LATITUDE <- 0 

for (i in 1:1000) {
  output <- geo_code(resale$address[i])

  resale$X[i] <- output$results.X
  resale$Y[i] <- output$results.Y
  resale$LONGITUDE[i] <- output$results.LONGITUDE
  resale$LATITUDE[i] <- output$results.LATITUDE
}

5.6.3.3 For loop to apply function (row 1001 and beyond)

• This code chunk is similar to the one above in Section 5.6.3.2.
• The only difference is, each time the for loop is ran, we have to change it to an interval of 1000. i.e. 1st run - 1001:2000, 2nd run - 2001:3000, 3rd run - 3001:4000 etc., until 15901
• We have to run multiple times (with interval of 1000) as Rstudio hangs if the entire 15901 rows are being ran at the same time.
• The code chunk below only shows the last run (15001:15901)

for (i in 15001:15901) {
  output <- geo_code(resale$address[i])
  
  if (resale$X[i] == 0) {
    resale$X[i] <- output$results.X
    resale$Y[i] <- output$results.Y
    resale$LONGITUDE[i] <- output$results.LONGITUDE
    resale$LATITUDE[i] <- output$results.LATITUDE
  }
}

5.6.3.4 Write into .csv file

• write_CSV() of readr package to write combined data set as a .CSV file

write_csv(resale, "data/aspatial/final_resale_prices_XY_LongLat.csv")

5.6.4 Import .csv file

• read_CSV() of readr package to import the above exported .CSV file
• glimpse() of dplyr package to take a look at our dataset

resale_new <- read_csv("data/aspatial/final_resale_prices_XY_LongLat.csv")
glimpse(resale_new)

Results above show that:

• There are 15901 rows and 16 columns in resale dataset.

5.6.5 Extract necessary columns

• select() of dplyr package to extract necessary columns

resale_new <- resale_new %>%
  select(month, town, flat_type, storey_range, floor_area_sqm, remaining_lease, resale_price, address, LONGITUDE, LATITUDE)

5.6.6 Manipulate storey_range column

• mutate() of dplyr package to create yesno column with values 1
• pivot_wider() of tidyr package to create columns from storey_range and input 1 or 0 (dummy variable)

resale_new <- resale_new %>%
  mutate(yesno = 1) %>%
  distinct %>%
  pivot_wider(names_from = storey_range, values_from = yesno, values_fill = 0)

5.6.7 Manipulate remaining_lease column

• gsub() of Base R to remove the words years and months in remaining_lease column

• substr() and substring() of Base R to place years and months in separate columns

• as.double() of Base R to convert to a double data type

• is.na() of Base R to locate NA values. Then, replace the NA values with 0.

• mutate() of dplyr to create a new column that contains the remaining lease calculated in years.

• Lastly, remove unnecessary columns:

  • names() of Base R to get names of resale_new data frame
  • Use %in% to drop columns specified in drop

resale_new$remaining_lease_new <- gsub("years", "", paste(resale_new$remaining_lease))
resale_new$remaining_lease_new <- gsub("month", "", paste(resale_new$remaining_lease_new))
resale_new$remaining_lease_new <- gsub("s", "", paste(resale_new$remaining_lease_new))

resale_new$remaining_lease_yr <- substr(resale_new$remaining_lease_new, start = 1, stop = 2)
resale_new$remaining_lease_mth <- substring(resale_new$remaining_lease_new, 5, 6)

resale_new$remaining_lease_yr <- as.double(resale_new$remaining_lease_yr)
resale_new$remaining_lease_mth <- as.double(resale_new$remaining_lease_mth)


resale_new$remaining_lease_mth[is.na(resale_new$remaining_lease_mth)] <- 0

resale_new <- resale_new %>%
  mutate(`remaining_lease_final` = `remaining_lease_yr` + round((`remaining_lease_mth`/12),2))

drop <- c("remaining_lease_new", "remaining_lease_yr", "remaining_lease_mth")
resale_new <- resale_new[, !names(resale_new) %in% drop]

5.7 Prepare prisch (primary school) Dataset

prisch dataset has a section on its own as there are different preparation steps to be done:

• Geo-code to extract its latitude and longitude
• Verify if all latitude and longitude have been extracted. If not, assign them
• Filter good primary school

5.7.1 Apply geo_code function

This code chunk:

• Assigns 0 to Longitude and Latitude column in prisch
• For loop to apply geo_code function defined in Section 5.6.3.1 on the prisch dataframe
• tryCatch() of Base R for the code to continue running even when there is error in the geo coding.
• Assigns the extracted longitude and latitude into the respective columns, back to prisch dataframe

prisch$LONGITUDE <- 0 
prisch$LATITUDE <- 0 

count <- 0
failed_count <- 0

for (i in 1:183){
  tryCatch( {
    output <- geo_code(prisch$address[i])
    count <- count + 1
    prisch$LONGITUDE[i] <- output$results.LONGITUDE
    prisch$LATITUDE[i] <- output$results.LATITUDE

  }, error = function(err) {
      count <- count + 1
      failed_count <- failed_count + 1
      cat('Failed to extract',count,'out of',length(prisch$address),'addresses')
    }
  )
}

5.7.2 Write output into a CSV file

• write_CSV() of readr package to write combined data set as a .CSV file

write_csv(prisch, "data/aspatial/prisch.csv")

5.7.3 Import prisch Dataset

• read_CSV() of readr package to import the above exported .CSV file
• glimpse() of dplyr package to take a look at our dataset

prisch <- read_csv("data/aspatial/prisch.csv")
glimpse(prisch)

Results above show that:

• There are 183 rows and 5 columns in prisch

5.7.4 Verify that all primary schools have Latitude & Longitude

5.7.4.1 Find primary schools with missing Latitude & Longitude

• There might be schools with missing latitude and/or longitude since in Section 5.7.1, a tryCatch() is ran.
• Hence, this code is to check if there are primary schools with missing latitude and/or longitude

prisch$school_name[prisch$LONGITUDE==0.0000]

Results above show that:

• There are indeed 4 schools, namely, HOUGANG PRIMARY SCHOOL, JING SHAN PRIMARY SCHOOL, WEST GROVE PRIMARY SCHOOL and WHITE SANDS PRIMARY SCHOOL with missing Latitude & Longitude.

5.7.4.2 Assign Latitude & Longitude

• Get Latitude & Longitude from: gps-coordinates.net
• HOUGANG PRIMARY SCHOOL’s Long & Lat: 103.881072, 1.3783581
• JING SHAN PRIMARY SCHOOL’s Long & Lat: 103.8520152, 1.3722578
• WEST GROVE PRIMARY SCHOOL’s Long & Lat: 103.6989833, 1.3446809
• WHITE SANDS PRIMARY SCHOOL’s Long & Lat: 103.9612546, 1.365473
• Assign the lat and long to the respective schools.

prisch$LONGITUDE[prisch$school_name == "HOUGANG PRIMARY SCHOOL"] <- 103.881072
prisch$LATITUDE[prisch$school_name == "HOUGANG PRIMARY SCHOOL"] <- 1.3783581

prisch$LONGITUDE[prisch$school_name == "JING SHAN PRIMARY SCHOOL"] <- 103.8520152
prisch$LATITUDE[prisch$school_name == "JING SHAN PRIMARY SCHOOL"] <- 1.3722578

prisch$LONGITUDE[prisch$school_name == "WEST GROVE PRIMARY SCHOOL"] <- 103.6989833
prisch$LATITUDE[prisch$school_name == "WEST GROVE PRIMARY SCHOOL"] <- 1.3446809

prisch$LONGITUDE[prisch$school_name == "HWHITE SANDS PRIMARY SCHOOL"] <- 103.9612546
prisch$LATITUDE[prisch$school_name == "WHITE SANDS PRIMARY SCHOOL"] <- 1.365473

5.7.5 Filter good primary school

• filter() of dplyr package to filter out good primary schools using the column gifted_ind
• The gifted_ind column refers to the school that are offered the Gifted Education Programme

gd_prisch <- prisch %>%
  filter(gifted_ind == "Yes")

Results above show that:

• There are 8 primary schools that are offered the Gifted Education Programme

6 Geospatial Wrangling

Note: This section will not be ran except for Section 6.5 and Section 6.6 to save computational time. Documentation on the results are still written even though the output is not shown.

The variables that we will prepare in this section are:

Locational factors

• Proximity to CBD
• Proximity to eldercare
• Proximity to hawker centres
• Proximity to MRT
• Proximity to park
• Proximity to good primary school
• Proximity to shopping mall
• Proximity to supermarket
• Numbers of kindergartens within 350m
• Numbers of childcare centres within 350m
• Numbers of bus stop within 350m
• Numbers of primary school within 1km

We will then combine the above variables with resale dataset which consists of the prepared Structural factors such as:

• Area of the unit
• Floor level
• Remaining lease

6.1 Convert Aspatial Dataframe into a sf object

6.1.1 Function to convert aspatial dataframe into a sf object

This function does the following:

• st_as_sf() of sf package to convert the data frame into a simple feature data frame
• st_transform() of sf package to convert the coordinates from wgs84 (i.e. crs:4326) to svy21 (i.e. crs=3414).

convert_sf <- function(df, x, y) {
  st_as_sf(df,
            coords = c(x, y),
            crs=4326) %>%
  st_transform(crs=3414)
}

6.1.2 Apply function to convert aspatial dataframes into a sf object

• Apply convert_sf function defined in Section 6.1.1 to the data sets

resale_sf <- convert_sf(resale_new, "LONGITUDE", "LATITUDE")
eldercare_sf <- convert_sf(eldercare, "Lng", "Lat")
hawker_sf <- convert_sf(hawker, "Lng", "Lat")
park_sf <- convert_sf(park, "Lng", "Lat")
gd_prisch_sf <- convert_sf(gd_prisch, "LONGITUDE", "LATITUDE")
mall_sf <- convert_sf(mall, "longitude", "latitude")
supermarket_sf <- convert_sf(supermarket, "Lng", "Lat")
kindergarten_sf <- convert_sf(kindergarten, "Lng", "Lat")
childcare_sf <- convert_sf(childcare, "Lng", "Lat")
prisch_sf <- convert_sf(prisch, "LONGITUDE", "LATITUDE")

6.2 Prepare Independent Variables

6.2.1 Central Business District (CBD) of Singapore

• Downtown Core is one of the central districts of Singapore.
• Its latitude and longitude are 1.287953 and 103.851784 respectively.
• st_as_sf() of sf package to convert the data frame into a simple feature data frame
• st_transform() of sf package to convert the coordinates from wgs84 (i.e. crs:4326) to svy21 (i.e. crs=3414).

longitude <- 103.851784
latitude <- 1.287953

cbd_coorinates_sf <- data.frame(longitude, latitude) %>%
  st_as_sf(., coords = c("longitude", "latitude"), crs=4326) %>%
  st_transform(crs=3414)

6.2.2 Function to calculate proximity of variables

This function does the following:

• st_distance() of sf package to calculate distance between 2 sf objects, with a matrix being the output

• drop_units() of units package to remove the units

• data.frame() of Base R to convert matrix into a dataframe

• rowMins() of matrixStats package to get the minimum value of each row i.e. shortest distance of variable to each HDB resale flat.

  • Another method; apply() of Base R, with argument MARGIN = 1 to apply to every row and FUN = min can also be used to get the minimum value of each row but rowMins() is faster

calulate_prox <- function(df1, df2, var) {
  distance_matrix <- st_distance(df1, df2) %>%
    drop_units()
  df1[,var] <- rowMins(distance_matrix)

  return(df1)
}

6.2.3 Apply function to calculate proximity

• Apply the function defined in Section: 6.2.2 to calculate proximity

resale_sf <- calulate_prox(resale_sf, cbd_coorinates_sf, "cbd_prox") %>%
              calulate_prox(., eldercare_sf, "eldercare_prox") %>%
              calulate_prox(., hawker_sf, "hawker_prox") %>% 
              calulate_prox(., mrt_sf, "mrt_prox") %>%
              calulate_prox(., park_sf, "park_prox") %>%
              calulate_prox(., gd_prisch_sf, "gd_prisch_prox") %>%
              calulate_prox(., mall_sf, "mall_prox") %>%
              calulate_prox(., supermarket_sf, "supermarket_prox") 

6.2.4 Function to calculate number of variables within a certain distance

This function does the following:

• st_distance() of sf package to calculate distance between 2 sf objects, with a matrix being the output
• drop_units() of units package to remove the units
• data.frame() of Base R to convert matrix into a dataframe
• rowSums() of Base R to get number of variables within a certain distance

calculate_num <- function(df1, df2, distance, var) {
  distance_matrix <- st_distance(df1, df2) %>% 
    drop_units()
  distance_matrix <- data.frame(distance_matrix)
  df1[,var] <- rowSums(distance_matrix <= distance)
  
  return(df1)
}

6.2.5 Apply function to calculate number of variables within a certain distance

• Apply the function defined in Section: 6.2.4 to calculate number of variables within a certain distance

resale_sf <- calculate_num(resale_sf, kindergarten_sf, 350, "kindergarten_num") %>%
              calculate_num(., childcare_sf, 350, "childcare_num") %>%
              calculate_num(., bus_sf, 350, "busstop_num") %>%
              calculate_num(., prisch_sf, 1000, "prisch_num")

6.3 Re-arrange columns in resale_sf

• Re-arrange columns such that all independent variables are at the back of the data frame.
• This will aid us in calibrating the model in the later steps.

col_order <- c("month", "town", "flat_type", "remaining_lease", "address",
              "resale_price", "floor_area_sqm", "remaining_lease_final", 
              "01 TO 03", "04 TO 06", "07 TO 09", "10 TO 12", "13 TO 15", "16 TO 18",
              "19 TO 21", "22 TO 24", "25 TO 27", "28 TO 30", "31 TO 33", "34 TO 36",
              "37 TO 39", "40 TO 42", "43 TO 45", "46 TO 48", "49 TO 51",
              'cbd_prox', "eldercare_prox", "hawker_prox", "mrt_prox", "park_prox",
               "gd_prisch_prox", "mall_prox", "supermarket_prox",
              "kindergarten_num", "childcare_num", "busstop_num", "prisch_num", "geometry")
resale_sf <- resale_sf[, col_order]

glimpse(resale_sf)

6.4 Write to a shp file

• st_write() of sf package to write into a shp file.

st_write(resale_sf, "data/geospatial/final_resale.shp")

6.5 Import shp file

• st_read() of sf package to import the geospatial data set.
• The imported shapefile will be a simple feature object of sf.

resale_sf <- st_read(dsn="data/geospatial", layer="final_resale")

Reading layer `final_resale' from data source 
  `C:\wlwong2018\IS415 Blog\_posts\2021-11-06-take-home-exercise-3\data\geospatial' 
  using driver `ESRI Shapefile'
Simple feature collection with 15853 features and 37 fields
Geometry type: POINT
Dimension:     XY
Bounding box:  xmin: 11597.31 ymin: 28217.39 xmax: 42623.63 ymax: 48741.06
Projected CRS: SVY21 / Singapore TM

6.6 Rename columns

• rename() of dplyr package to rename columns for easy visualisation.

resale_sf <- resale_sf %>%
  dplyr::rename(resale_price = rsl_prc, floor_area_sqm = flr_r_s, remaining_lease_final = rmnng__,
         lvl_01_TO_03 = X01TO03, lvl_04_TO_06 = X04TO06, lvl_07_TO_09 = X07TO09,
         lvl_10_TO_12 = X10TO12, lvl_13_TO_15 = X13TO15, lvl_16_TO_18 = X16TO18,
         lvl_19_TO_21 = X19TO21, lvl_22_TO_24 = X22TO24, lvl_25_TO_27 = X25TO27,
         lvl_28_TO_30 = X28TO30, lvl_31_TO_33 = X31TO33, lvl_34_TO_36 = X34TO36,
         lvl_37_TO_39 = X37TO39, lvl_40_TO_42 = X40TO42, lvl_43_TO_45 = X43TO45,
         lvl_46_TO_48 = X46TO48, lvl_49_TO_51 = X49TO51,
         cbd_prox = cbd_prx, eldercare_prox = eldrcr_, hawker_prox = hwkr_pr,
         mrt_prox = mrt_prx, park_prox = prk_prx, gd_prisch_prox = gd_prs_,
         mall_prox = mll_prx, supermarket_prox = sprmrk_, kindergarten_num  = kndrgr_,
         childcare_num  = chldcr_, busstop_num  = bsstp_n, prisch_num  = prsch_n)

7 Exploratory Data Analysis

In this section, we will perform some Exploratory Data Analysis to understand our dataset.

7.1 EDA using statistical graphics

7.1.1 Function to Plot Histogram

• geom_histogram() of ggplot package to plot a histogram to see the distribution of resale_price

mul_hist <- function(df, vnam, x_axis) {
  ggplot(data=df, aes(x=vnam)) +
  geom_histogram(bins=20, color="black", fill="salmon") +
        scale_x_continuous(name = x_axis)
}

7.1.2 Plot distribution of resale_price

• Use function created in Section 7.1.1 to plot histogram

mul_hist(resale_sf, resale_sf$resale_price, "Resale Price")

Results above show that:

• The histogram is right-skewed, implying that more HDB flats were transacted at relative lower prices.

7.1.3 Normalise using Log Transformation

• Statistically, the skewed distribution can be normalised by using log transformation.
• Use mutate() and log of dplyr package to derive a new variable called resale_price_log by using a log transformation on the variable resale_price

resale_sf <- resale_sf %>%
  mutate(`resale_price_log` = log(resale_price))

7.1.4 Plot resale_price_log

• Apply function created in Section 7.1.1 to plot histogram with column resale_price_log

mul_hist(resale_sf, resale_sf$resale_price_log, "Resale Price Log")

Results above show that:

• The distribution is relatively less skewed after the transformation.